1. Field of the Invention
This invention relates to irradiation-sterilizable medical articles.
More particularly, it is concerned with irradiation-sterilizable medical articles molded from propylene polymer compositions in which stabilizers are incorporated.
Propylene polymers, which have characteristic transparency, rigidity, impact strength and other properties, are widely used for medical articles, especially for disposable medical articles such as syringes, needle bases, infusion or blood transfusion sets, and instruments for blood collection. Propylene polymer products, however, have a disadvantage of being deteriorated or degradated by irradiation sterilization. When subjected to radiation at a dose from 2 to 4 Mrad., propylene polymers will undergo degradation or deterioration reactions thereby causing discoloration, cracking, reduction in impact strength in the product. Moreover, there will occur such problems as elution of the stabilizers incorporated into the polymer for inhibition of the oxidation, removal of the radicals and other objectives, development of odors and marked coloration. If the medical article is a product of injection molding, the deterioration caused by irradiation as set forth above will be especially remarkable.
2. Description of the Prior Art
Several processes have heretofore been reported for improving radiation resistance of the propylene polymer products.
It has been proposed to incorporate into the propylene polymers a variety of phenol, phosphorus or sulfur compounds as the stabilizer (U.S. Pat. No. 3,940,325), to incorporate hindered amines (European Patent Laid Open No. 7736) and to incorporate non-crystalline additives into propylene polymers with a narrower molecular weight distribution (U.S. Pat. No. 4,274,932). Although the radiation resistance of propylene polymers are considerably improved by these methods, there remains room for further improvement.
As a matter of fact, the incorporation of phenol, phosphorus or sulfur compounds is not satisfactory for practical use in coloration resistance, resistance to heat deterioration, as well as due to the elution phenomenon into the content that is contacted with the molded article. For example, the product to which tetrakis[methylene(3,5-di-t-butylhydroxyhydrocinnamate)]methane described in the above-mentioned U.S. Pat. No. 3,940,325 is added will be remarkably colored by gamma irradiation at a dose of 2.5 Mrad. The product to which 1,1,3-tris(2-methyl-5-t-butyl-4-hydroxyphenol)butane is added will also have unsatisfactory heat resistance after irradiated.
Addition of hindered amines, for example, di-(2,2,6,6-tetramethyl-4-piperidyl) sebacate, a hindered amine described in the above-mentioned European Patent Laid Open No. 7736 is associated with such problems as elution of the cytotoxic substances and bleeding of such additive onto the surface of the molded article during aging. Addition of the hindered amine alone will also result in reduction in molecular weight during molding thereby much decreasing the strength.
Also, the incorporation of non-crystalline additives in propylene polymers of a narrower molecular weight distribution is not practically usable because of unsatisfactory inhibition of deterioration as well as due to problematic bleeding and toxicity of the additives.
As described above, any of the heretofore reported processes have disadvantages in some respects so that they are not satisfactory for commercial use.
It is a general procedure to add a nucleating agent to propylene polymer compositions for improving transparency of the product. Dibenzylidenesorbitol, which is a nucleating agent excellent in transparency-improving effect among the nucleating agents presently available, will be degradated by irradiation and develop odors. Therefore, irradiation sterilization of medical articles containing this nucleating agent has not been acceptable.